The present invention relates, in general, to wireless communications systems, and more particularly, to a method for transceiving digital data through a voice channel of digital wireless communications network.
Generally, a voice communications system in a digital wireless communications network uses an encoding and decoding algorithm suitably optimized for voice characteristics so as to efficiently send an exact voice. Preferably, a vocoder performs an encoding and decoding of voice in such a wireless voice communications system. The vocoder suitably converts the voice into a digital signal through linear prediction coding algorithms which usually uses the linear feature of voice. Additionally, besides the linear prediction coding algorithm for converting the voice, by having an additional algorithm for removing an interference which is not the voice or by having a linear prediction coding algorithm including an algorithm which can remove the interference, most vocoders can improve the quality of the voice communications system.
The linear prediction coding algorithm of a vocoder suitably predicts and evaluates the voice characteristic of a given section according to the linear characteristics of voice, and then, codes the characteristic with contraction. It assigns many contraction data bits and codes in detail in a section where the voice is highly changed or the voice exists abundantly, while assigning small contraction data bit and roughly codes in a section having non-linear characteristics and monotonous characteristics. Moreover, in some cases, the change in a section having non-linear characteristics and monotonous characteristics can be suitably removed through a noise elimination algorithm.
The digital wireless telecommunications network is required to send not only a simple voice but also data on a real time basis. Particularly, since a voice channel which is used to send a voice has a relatively larger bandwidth in comparison with other channels in the wireless telecommunications system, if it sends data by using the voice channel, it can send much more high-capacity data on a real time basis. However, data which are made by the random repetition of 0 and 1 and, resultantly, must have a non-linear form should be different from the voice having linear characteristics. In case of encoding and decoding the data through the linear prediction coding algorithm of a vocoder, the data can be easily distorted due to the property difference of the voice and data. Accordingly, a data communications algorithm for preventing the distortion in the process of encoding and decoding the data is required for the vocoder so as to send the data by using a vocoder which performs the encoding and decoding of the voice. Hereinafter, the method for transceiving data by using a voice channel in a digital wireless telecommunications network will be illustrated in detail.
FIG. 1 is a conceptual diagram for illustrating an exemplary wireless communications network which provides an in-band signaling (IBS) according to a conventional technology.
As shown, the wireless communications network preferably includes a terminal 14 for suitably transmitting a voice signal 31 encoded through a voice channel 34 and a base station 36 for suitably receiving the voice signal 31 transmitted from the terminal 14. Preferably, the voice signal 31 transmitted through the base station 36 is suitably changed to be transmitted through a cellular telecommunication switching system (CTSS) 38 through a wired network.
Preferably, a voice 22 transmitted from a user 23 of the terminal 14 is suitably encoded through the vocoder 18 which is included within the terminal 14. The encoded voice signals are transmitted to Public Switched Telephone Network (PSTN) 42 through the digital voice channel 34 via the base station 36, and then suitably transmitted to the terminal which the other user uses through the PSTN 42. If it is decoded in the vocoder within the terminal which the other user uses, the transmission of the voice through the wireless communications network is suitably completed.
When data is inputted from a data source 30 through the vocoder 18, there can be a difference in that it is converted to an audio signal 26 similar to the voice 22 via an in-band signaling modem 28 before being encoded through the vocoder 18. Thereafter, the audio signal 26 converted through the in-band signaling modem 28 is suitably encoded through the vocoder 18, and transmitted to the cellular telecommunication switching system 38 through the voice channel 34. When data is inputted from the data source 30, it can be suitably transmitted to a server 40 which is in a destination location through an IP network 46, or can be suitably transmitted to a terminal which the other user uses through the PSTN 42. Preferably, the server 40 includes an ISB modem 28, so that it can decode a signal encoded by the vocoder 18.
FIG. 2 is a block diagram for illustrating an exemplary preferred structure of encoder 52 within an in-band signaling modem 28 illustrated in FIG. 1.
As shown, an encoder 52 of the in-band signaling modem 28 preferably includes a data buffer 58, a packetizer 60, a packet formatter 62 and an IBS modulator 64. Preferably, data inputted from the data source 30 are suitably divided by the packetizer 60 with a given size unit of a packet payload following a packet header. Preferably, the packet formatter 62 adds a packet preamble or a packet postamble for suitably preventing the deformation of the packet payload and suitably enhancing the transmission efficiency. Preferably, the IBS modulator 64 modulates by using two or more different tone frequencies 66, 68 so as to generate the audio signal 26 having features similar to the voice 22 through receiving a IBS packet 70 outputted from the packet formatter 62.
The operation of the in-band signaling modem 28 can be illustrated with both of the encoding and the decoding. For example, in the transmission side, the IBS packet 70 is suitably encoded with two different complex tones 66, 68 which indicates bit 0 and bit 1 used in a frequency band between 400 Hz and 1000 Hz and transmitted. Preferably, in the receiving side, the decoder configures a signal-noise ratio (SNR) with an energy ratio of an in-band filter of a band in which complex tones are suitably formed from an input audio signal to an out-of-band filter in which complex tones does not exist, and decodes the payload after activating the IBS modem and exactly synchronizing from a sync pattern when this value exceeds a critical point.
FIG. 3 is a conceptual diagram for illustrating a preferred exemplary configuration of the IBS packet 70 illustrated in FIG. 2.
As shown, the IBS packet 70 preferably includes a preamble 73 consisting of a sacrifice bit 71, a header 72 and a sync pattern 74, a postamble 79 including a sacrifice bit 75, a payload 76 and a checksum 78. The sacrifice bit 71, 75 in the front and the rear of IBS packet 70 suitably prevents an automatic gain controller (AGC) of the vocoder 18 of the terminal 14 from distorting the payload. Preferably, the sync pattern 74 prevents the vocoder 18 from transforming the payload by generating signals similarly with the voice signal through the arrangement of 0 and 1. In some cases, the distortion of the payload through an adaptable filter within the vocoder 18 can be suitably reduced by inserting some bits of the payload 76 into the preamble 73.
When data having the nonlinear feature are encoded by using the vocoder 18, there still exists a probability that the data can be distorted and contracted. To prevent this problem, the conventional method for inserting a pattern where ‘0’ or ‘1’ is arranged or inserting a meaningless sacrifice bit in the front or rear of the packet is preferably used. However, the insertion of a specific pattern or a meaningless sacrifice bit into data having the nonlinear feature does not mean that the data have similar characteristics to the voice. Accordingly, there still exists a probability that the data can be distorted and contracted in the encoding process through the vocoder 18.
The above information disclosed in this the Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.